In many applications, particularly those involving electronic or optical materials, it is frequently desirable to adhere two substrates together in a manner that avoids substantially altering the properties of the substrates at their interface.
There are a variety of ways of adhering two substrates together. One common method involves coating a surface of at least one of the substrates with a relatively thick layer of an adhesive prior to bringing the substrates into contact. While this method may produce a joint with good mechanical strength, the presence of the layer of adhesive may alter, sometimes dramatically, the physical characteristics of the substrates or the substrate-substrate interface. This can be a particular problem in electronic applications which have exacting requirements and often entail bonding very thin sheets of material.
Van der Waals forces have been utilized to bond two substrates together without the addition of an adhesive. Van der Waals forces, however, are relatively weak and are easily disrupted by environmental contaminants. To achieve any significant bonding by dispersion forces alone requires exceedingly clean, exceedingly smooth surfaces. In addition, van der Waals forces drop off rapidly with separation (e.g., decrease as 1/D.sup.3 for two flat planes, where D is distance). These factors make the range of applications and materials to which bonding based on van der Waals forces can be applied, extremely limited.
Acid-base interactions offer the potential to form a stronger, less environmentally sensitive adhesive bond, i.e., an adhesive bond which is less sensitive to the presence of contaminants. Thus far, this approach has been confined to the application of relatively thick interaction layers onto substrates, to interdiffused polymers, and to polymer-surface adhesion (e.g., the enhancement of the adhesion of paints or coatings to a metal substrate). All of these techniques can substantially alter the physical characteristics of the adhered substrates and/or the article produced. In particular, these methods of adhering substrates may substantially alter the dielectric, optical, thermal or mechanical properties of the substrates or of the substrate-substrate interface.
It is therefore an object of the invention to provide a method of adhering substrates to form an article without substantially altering the physical characteristics of the substrates. More particularly, it is an object of the invention to provide a method of adhering substrates which does not substantially alter the dielectric, optical, thermal or mechanical properties of the substrates in the vicinity of the substrate-substrate interface.
It is a further object of the invention to provide an article including two substrates, which are strongly bonded together despite the lack of a discrete, substantial adhesive layer between the substrates.
It is another object of the invention to provide a method of adhering two substrates, which have substantially identical physical properties, to construct an article. For example, the method permits the adhering substrates, which are formed from identical material, to form an article which has very similar physical properties to that of a single substrate formed from the material.
It is yet another object of the invention to provide a method of adhering substrates in such a manner that the substrates may be separated and readhered without any further application of an adhesive. Further, another object is to provide a method of adhering substrates that forms an adhesive bond between the substrates that is capable of reforming after rupture due to shear.
These and other objects and advantages of the present invention will be apparent from the description of the invention which follows.